Development of Scroll Compressors for R410A

Transcription

1 Purdue University Purdue e-pubs International Compressor Engineering Conference School of Mechanical Engineering 2004 Development of Scroll Compressors for R410A Nobuhiro Nojima Takahiro Uematsu Takashi Uekawa Katsumi Hirooka Follow this and additional works at: Nojima, Nobuhiro; Uematsu, Takahiro; Uekawa, Takashi; and Hirooka, Katsumi, "Development of Scroll Compressors for R410A" (2004). International Compressor Engineering Conference. Paper This document has been made available through Purdue e-pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu for additional information. Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at Herrick/Events/orderlit.html

2 C035, Page 1 Development of Scroll Compressors for R410A Nobuhiro Nojima, Takahiro Uematsu, Takashi Uekawa, Katsumi Hirooka Compressor Development and Engineering Group, Air-Conditioning Manufacturing Division,, Ltd Chikko-Shinmachi, Sakai, Osaka, , Japan Tel: Fax: nobuhiro.nojima@daikin.co.jp ABSTRACT We have completed development of the new scroll compressors for R410A by upgrading our existing airconditioners scroll compressors. We have incorporated our various technologies into developing these R410A new scroll compressors and have succeeded in several major achievements, including: 1) Optimization of the orbiting scroll back pressure force, which reduces the thrust bearing loss; 2) Optimization of the scroll wrap dimension, which achieves high COP; 3) Improvement of shell strength, which endures 15.2MPa high side pressure. 1. INTRODUCTION More and more of R410A is being used in air-conditioners lately to improve performance, given that R410A can decrease refrigerant pressure loss by reducing the volume flow rate. This market trend has given rise to an urgent need to develop a high-efficiency compressor for R410A. The highefficiency scroll compressors for R22/ R407C, which have a unique high/low pressure side structure, are being manufactured annually. Using this R407C compressor as the base allowed us to develop a high-efficiency R410A compressor over a shorter development period at a lower investment. There were, however, three technical problems to resolve: 1) Thrust bearing loss needed to be reduced to achieve high efficiency. 2) Scroll wrap dimension needed to be optimized to resist the higher pressure. 3) Shell strength needed to be increased to resist the higher pressure. We have confirmed that the following three technologies provide as effective measures to resolve these issues: 1) Asymmetrical scroll wraps 2) Non-uniform thickness scroll wraps 3) Modified shell shape In the last section, we show that the R410A high-efficiency compressor which uses these technologies. 2. Structure of compressors The development model was based on a scroll compressor with a high/low pressure side shell structure, as shown in Figure 1. This structure has the following four characteristics. 1) The scroll compressor has a high/low pressure side shell structure, with the motor located in the high-pressure side and the compressed element is in the low-pressure side. 2) It has an asymmetrical scroll wraps and non-uniform thickness scroll wraps. 3) Is has the axial and radial compliance mechanism. 4) All of discharge gas is let flow from the orbiting scroll into the gas passage of the crank shaft and it is let flow through the effective oil separator to lower side of a motor. The next section describes the new technologies for R410A that have been developed.

3 C035, Page 2 3. Developments 3.1 Reduction in thrust bearing loss This compressor is structured so that the orbiting scroll is pressed against the fixed scroll by the high-pressure gas supplied to the back of the orbiting scroll (as shown in Figure 2), so that leakage in the scroll is reduced. The thrust bearing loss is determined by sliding speed and pressure force: therefore, both need to be decreased. Reduction in the sliding speed It is widely known that a smaller orbiting radius will effectively decrease the sliding speed. However, there are several restrictions involved in making the orbiting radius smaller, as shown in Figure 3, including the limited scroll strength because of higher scroll wraps and limited discharge passage area because of the smaller scroll. Figure 3 shows the relationship between the orbiting radius and the compressor loss. The smaller the orbiting radius, the smaller the thrust bearing loss. On the other hand, however, the smaller discharge passage increases pressure loss, resulting in minimum value. The scroll strength limitation also had to be considered to minimize the orbiting radius. Applying the specifications for R407C compressor without modification resulted in locating point A indicated in Figure 3. This meant that the orbiting radius could be made smaller. From these observations, it was determined that locating the orbiting radius for R410A compressor at point B would significantly reduce the sliding speed. As a result, the loss was decreased 3% against that for R407C compressor. This relationship can also be applied to other compressors to optimize the orbiting radius. Reduction in the orbiting scroll back pressure force When the orbiting scroll back pressure force is too large, friction loss increases. On the other hand, when the orbiting scroll back pressure force is too small, leakage loss increases. The orbiting scroll back pressure force for this compressor was optimized using the following method. Figure 4 shows the relationship between the orbiting scroll back pressure force and the compressor loss, the coefficient of tipping. It was found from Figure 4 that when the orbiting scroll back pressure force in the axial direction is reduced, compressor loss can be decreased because of the reduction in thrust bearing loss. When a certain the coefficient of tipping is exceeded, however, the scrolls start separating, and an abrupt increase in loss is seen. To improve this situation, an asymmetrical scroll wrap was also applied to this compressor to lower the overall the coefficient of tipping, achieving a 1% reduction in compressor loss compared to a symmetrical scroll wrap. 3.2 Optimization of scroll wrap dimension Because the pressure is higher with the use of R410A, the orbiting radius cannot be made smaller using the scroll wrap dimension designed for R407C compressor because of the limitation of the scroll strength. To solve this problem, non-uniform thickness scroll wraps, which increase its thickness gradually from out side to inside, was further improved. This modification increased the rate of the change in thickness so that the scroll inside, where scroll strength would be insufficient because of the increased pressure, was thicker than for the R407C compressor. The improving scrolls, as shown in the analysis results in Figures 5 and 6, ensured sufficient safety factor against the higher pressure of R410A. Although the discharge port area had to be decreased because of this modification, the port area equivalent to that for R407C compressor could be maintained by adapting the modified scroll shape, as shown in Figure 7. Now, both sufficient scroll strength and the discharge port area were secured. 3.3 Shell strength improvement The technical problem occurred when we t ried to increase the shell strength to resist the higher pressure with the use of R410A, a crack in the joint that connects the hermetic terminal and the shell. Figure 8 is a detail of the terminal section. A flat area was created to fit the terminal to the shell, then projection welding was done to attach and seal the terminal in that area. Next, the dynamic model shown in Figure 9 was invented to locate the cause of this problem. Figure 9 shows that when a larger flat area height is set, moment B increases in the opposite direction to offset moment A, thus decreasing the stress.

4 C035, Page 3 We also conducted a strength analysis, as shown in Figure 10, and pressure tests using the actual model by gradually changing the flat area height in order to verify our assumption. The results are shown in Figure 11. As can be seen in this figure, as the flat area height is increased, the shell strength increases, however, the strength begins to drop when it reaches a certain height. This is because the shell strength around the terminal declined due to the thinner shell thickness. From our study of the above, we have found that the shell strength can be improved by increasing the terminal flat area height, and that there is an optimum point for the flat area height. 3.4 The compressor for R410A We developed the compressor with compression efficiency equivalent to that of the base model. The specifications of this compressor are shown in Table CONCLUSIONS We can conclude that it is beneficial to use the following designs for Scroll Compressors for R410A in order to improve on the scroll compressors for R407C. The optimum orbiting radius that minimizes the thrust sliding speed was able to select by fully understanding the relationship between the orbiting radius and the compressor loss (the thrust bearing loss and the pressure loss of discharge). Use of the asymmetrical scroll wrap was effective in reducing the orbiting scroll back pressure force in the axial direction. Optimizing the rate of thickness change of non-uniform thickness scroll wrap proved effective in order to maintain scroll strength against the higher pressure with R410A. Any resulting reduction in the discharge port area could be avoided by using a modified scroll wraps. Increasing the flat area height was effective in increasing the strength of the shell around hermetic terminal. REFERENCES [1] H. Kuroiwa, et al., Development of high-efficiency compressors with an alternative refrigerant, 1997 International Compression Technique Conference at Xi an. [2] K. Matsuba, et al., Development of Highly Reliable and Efficient Scroll Compressors. Proceedings of the 1998 Compressor Engineering Conference, Purdue University. [3] S. Hagiwara, et al., Development of Scroll Compressor of Improved High-Pressure-Housing. Proceedings of the 1998 Compressor Engineering Conference, Purdue University.

5 C035, Page 4 Fixed scroll Compressed gas load Thrust bearing loss Orbiting scroll Orbiting scroll back pressure force Figure 1 Compressor Cross Section Figure 2 Schematic diagram 460 Limit of scroll wrap strength B A Thrust bearing loss* 140 Pressure loss of discharge Orbiting radius *back pressure load is constant Figure 3 Relationship between the orbiting radius and the compressor loss

6 C035, Page Minimum pressure force (Asymmetric wraps) Minimum pressure force (Symmetric wraps) Limit line of Tipping Coefficient of tipping (Symmetric wraps) Coefficient of tipping (Asymmetric wraps) Coefficient of tipping Orbiting scroll back pressure force Figure 4 Relationship between the orbiting scroll back pressure force and the compressor loss Figure 5 Analysis result of high compression ratio Figure 6 Analysis result of low compression ratio Figure 7 Description of modified scroll shape

7 C035, Page 6 Flat area height Welded part Moment B Load on terminal Moment A Figure 8 Detail of the terminal section Load on shell Moment load on welded part Figure 9 Dynamic model on the welded part Terminal Shell Figure 10 Analysis result of the terminal flat area Ratio of shell strength(%) : Simulation o : Experiment Flat area height(mm) Figure 11 Relationship between the flat area height and the shell strength Capacity (Revolution speed) 11200W@60r/s (20~108r/s) Table 1: Specifications of development compressor COP Size Weight Power 4.11@60r/s Diameter: 168mm Height: 420mm 33.4kg DC Inverter COP condition: Tc/Te/Sh/Sc=42/3/5/8(Celsius)